Digitizer module, a waveform generating module, a converting method, a waveform generating method and a recording medium for recording a program thereof

ABSTRACT

A digitizer module comprises an AD converter for sampling a pair of analog signals at a predetermined time interval and converting into a first and second digital signals respectively, a second signal frequency component calculating unit for calculating a second signal frequency component representing a component of each frequency of the second digital signal on the basis of the second digital signal, a skew frequency component calculating unit for calculating a skew frequency component representing a phase error of each frequency of the second digital signal corresponding to the first digital signal on the basis of a skew of a timing with which the pair of analog signals are sampled by the AD converter and a second signal frequency component correcting unit for correcting the second signal frequency component on the basis of the skew frequency component.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a digitizer module, a waveformgenerating module, a converting method, a waveform generating method anda recording medium for recording a program thereof. More particularly,the present invention relates to a digitizer module for converting apair of analog signals into a pair of digital signals with equal sampletiming, a waveform generating module for outputting a pair ofsynchronous analog signals and a program and a method of processthereof.

2. Description of the Related Art

As known in the art, with regard to a digitizer module for sampling apair of analog signals such as quadrature modulated signals to besynchronized each other, there has been a problem that if samplingtimings of a pair of AD converters sampling a pair of analog signals donot match each other, quality of observed signals is lowered due to animpairment of orthogonality regarding a result of measuring the twoanalog signals originally in quadrature.

And also, with regard to a waveform generating module for converting apair of digital signals to be synchronized each other into analogsignals respectively and outputting the signals, if converting timingsof a pair of DA converters converting a pair of digital signals into apair of analog signals respectively do not match each other, quality ofoutputted signals is lowered due to a phase difference between a pair ofanalog signals, which are originally synchronized.

In order to prevent the impairment of quality of signal due to theprevious problems, an equal-length routing has been used with respect toa clock signal of a pair of DA converters or a pair of AD converters.

The difference of sample timing or converting timing previouslydescribed also results from differences between characteristics of ADconverters or DA converters and circuits or routing on other signaltrace. Consequently, in order to achieve a digitizer module or awaveform generating module with higher precision, it is desirable toprevent the impairment of quality of signal due to these causes, as wellas an equal-length routing with respect to a clock signal.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide adigitizer module, a waveform generating module, a converting method, awaveform generating method and a recording medium for recording aprogram thereof, which are capable of solving the problems above. Theabove and other objects can be achieved by combinations described in theindependent claims. The dependent claims define further advantageous andexemplary combinations of the present invention.

According to the first aspect of the present invention, a digitizermodule for converting a pair of analog signals into a pair of digitalsignals with equal sample timing, comprises an AD converter for samplingthe pair of analog signals at a predetermined time interval andconverting into a first and second digital signals respectively, asecond signal frequency component calculating unit for calculating asecond signal frequency component representing a component of eachfrequency of the second digital signal on the basis of the seconddigital signal, a skew frequency component calculating unit forcalculating a skew frequency component representing a phase error ofeach frequency of the second digital signal corresponding to the firstdigital signal on the basis of a skew of a timing with which the pair ofanalog signals are sampled by the AD converter and a second signalfrequency component correcting unit for correcting the second signalfrequency component on the basis of the skew frequency component.

A digitizer module may further comprise a corrected second signalcalculating unit for calculating the second digital signal on which theskew has been corrected on the basis of the second signal frequencycomponent, which is corrected.

The second signal frequency component calculating unit may calculate thesecond signal frequency component by performing a discreteFourier-transform on the second digital signal, the skew frequencycomponent calculating unit may calculate a correcting function in afrequency domain for correcting the skew with the skew frequencycomponent and the second signal frequency component correcting unit maycorrect the second signal frequency component by multiplying the secondsignal frequency component by the correcting function in the frequencydomain.

A digitizer module may further comprise a first signal frequencycomponent calculating unit for calculating a first signal frequencycomponent representing a component of each frequency of the firstdigital signal on the basis of the first digital signal, wherein thesecond signal frequency component correcting unit may correct the secondsignal frequency component on the basis of the skew frequency componentand the first signal frequency component.

A digitizer module may further comprise a second signal frequencycomponent calculating unit for calculating a first signal frequencycomponent representing a component of each frequency of the firstdigital signal on the basis of the first digital signal and a firstsignal frequency component correcting unit for correcting the firstsignal frequency component on the basis of the skew frequency component.

A digitizer may further comprise a skew measuring unit for measuring theskew on the basis of an amount of a phase difference between the firstand second digital signals, in case a same signal as the pair of analogsignals is inputted to the AD converter.

According to the second aspect of the present invention, a digitizermodule for converting a pair of analog signals into a pair of digitalsignals with equal sample timing, comprises an AD converter for samplingthe pair of analog signals at a predetermined time interval andconverting into a first and a second digital signals, a first digitalfilter for generating a first converted signal into which the firstdigital signal is converted on the basis of a predetermined filtercoefficient, a correcting filter coefficient generator for generating acorrecting filter coefficient correcting a skew, besides a waveform ofan impulse response of the correcting filter coefficient is same as thefirst digital filter, on the basis of the skew of a timing with whichthe pair of analog signals are sampled by the AD converter and apredetermined filter coefficient and a second digital filter forconverting the second digital signal on the basis of the correctingfilter coefficient and generating a second converted signal on which theskew is corrected.

The correcting filter coefficient generator may make the correctingfilter coefficient be h(k·T−τ), in case the predetermined filtercoefficient is h(k·T) and the skew is τ, where the first digital filterhas at least two the predetermined filter coefficient, k denotes aninteger in a range of zero to a number one less than the number of thepredetermined filter coefficient and T denotes a sampling interval ofthe AD converter.

According to the third aspect of the present invention, a waveformgenerating module for outputting a pair of synchronous analog signals,comprises a first digital signal calculating unit for generating a firstdigital signal on the basis of a first signal frequency componentrepresenting a component of each frequency of a first analog signal,which the waveform generating module should output, a second digitalsignal calculating unit for generating a second digital signal on thebasis of a second signal frequency component representing a component ofeach frequency of a second analog signal, which the waveform generatingmodule should output, a DA converter for converting the first and seconddigital signals into the first and second analog signals at apredetermined time interval respectively, a skew frequency componentcalculating unit for calculating a skew frequency component representinga phase error of each frequency of the second analog signalcorresponding to the first analog signal, on the basis of a skew of atiming with which the first and second digital signals are converted bythe DA converter and a second signal frequency component correcting unitfor correcting the second signal frequency component used for generatingthe second digital signal by the second digital signal calculating uniton the basis of the skew frequency component.

The skew frequency component calculating unit may calculate a correctingfunction in a frequency domain for correcting the skew with the skewfrequency component, the second signal frequency component correctingunit may correct the second signal frequency component by multiplyingthe second signal frequency component by the correcting function in thefrequency domain and the second digital signal calculating unit maygenerate the second digital signal by performing an inverse discreteFourier-transform on the second signal frequency component corrected bythe second signal frequency component correcting unit.

The second signal frequency component correcting unit may correct thesecond signal frequency component used for generating the second digitalsignal by the second digital signals calculating unit, on the basis ofthe skew frequency component and the first signal frequency component.

A waveform generating module may further comprise a first signalfrequency component correcting unit for correcting the first signalfrequency component used for generating the first digital signal by thefirst digital signal calculating unit, on the basis of the skewfrequency component.

A waveform generating module may further comprise a skew measuring unitfor measuring the skew on the basis of an amount of a phase differencebetween the first and second analog signals, in case a same signal asthe first and second digital signals is inputted to the DA converter.

According to the fourth aspect of the present invention, a waveformgenerating module for outputting a pair of synchronous analog signals,comprises a first digital filter for generating a first converted signalinto which a first digital signal, which represents a signal value of afirst analog signal to be outputted, is converted on the basis of afirst filter coefficient, a second digital filter for generating asecond converted signal into which a second digital signal, whichrepresents a signal value of a second analog signal to be outputted, isconverted on the basis of a second filter coefficient, a DA converterfor converting the first and second digital signals into the first andsecond analog signals at a predetermined time interval respectively anda correcting filter coefficient generator for generating the secondfilter coefficient correcting a skew, besides a waveform of an impulseresponse of the correcting filter coefficient is same as the firstdigital filter, on the basis of the skew of a timing with which the DAconverter converts the first and second digital signals into the firstand second analog signals and the first filter coefficient.

The correcting filter coefficient generator may make the second filtercoefficient be h(k·T−τ), in case the first filter coefficient is h(k·T)and the converting timing error is τ, where the first digital filter hasat least two the first filter coefficient, k denotes an integer in arange of zero to a number one less than the number of the first filtercoefficient and T denotes a converting interval of the DA converter.

According to the fifth aspect of the present invention, a recordingmedium for recording a program used for a digitizer module converting apair of analog signals into a pair of digital signals with equal sampletiming is provided, wherein the digitizer module comprises an ADconverter for sampling the pair of analog signals at a predeterminedtime interval and converting the pair of analog signals into a first andsecond digital signals, and the program allows the digitizer module tofunction with a second signal frequency component calculating unit forcalculating a second signal frequency component representing a componentof each frequency of the second digital signal on the basis of thesecond digital signal, a skew frequency component calculating unit forcalculating a skew frequency component representing a phase error ofeach frequency of the second digital signal corresponding to the firstdigital signal, on the basis of the skew of a timing with which the pairof analog signals are sampled by the AD converter and a second signalfrequency component correcting unit for correcting the second signalfrequency component on the basis of the skew frequency component.

According to the sixth aspect of the present invention, a convertingmethod for converting a pair of analog signals into a pair of digitalsignals with equal sample timing, comprises the steps of sampling thepair of analog signals at a predetermined time interval and convertingthe pair of analog signals into a first and second digital signalsrespectively, calculating a second signal frequency componentrepresenting a component of each frequency of the second digital signalon the basis of the second digital signal, calculating a skew frequencycomponent representing a phase error of each frequency of the seconddigital signal corresponding to the first digital signal, on the basisof the skew of a timing with which the pair of analog signals aresampled during the step of sampling and converting and correcting thesecond signal frequency component on the basis of the skew frequencycomponent.

According to the seventh aspect of the present invention, a recordingmedium for recording a program used for a digitizer module converting apair of analog signals into a pair of digital signals with equal sampletiming is provided, wherein the digitizer module comprises an ADconverter for sampling the pair of analog signals at a predeterminedtime interval and converting the pair of analog signals into a first andsecond digital signals, and the program allows the digitizer module tofunction with a first digital filter for generating a first convertedsignal into which the first digital signal is converted on the basis ofa predetermined filter coefficient a correcting filter coefficientgenerator for generating a correcting filter coefficient correcting askew, besides a waveform of an impulse response of the correcting filtercoefficient is same as the first digital filter, on the basis of theskew of a timing with which the first and second analog signals areconverted by the AD converter and the predetermined filter coefficientand a second digital filter for converting the second digital signal onthe basis of the correcting filter coefficient and generating a secondconverted signal on which the skew is corrected.

According to the eighth aspect of the present invention, a convertingmethod for converting a pair of analog signals into a pair of digitalsignals with equal sample timing, comprises the steps of sampling thepair of analog signals at a predetermined time interval and convertingthe pair of analog signals into a first and second digital signalsrespectively, generating a first converted signal into which the firstdigital signal is converted on the basis of a predetermined filtercoefficient, generating a correcting filter coefficient correcting askew, besides a waveform of an impulse response of the correcting filtercoefficient is same as the step of generating the first convertedsignal, on the basis of the skew of a timing with which the first andsecond analog signals are converted by the AD converter and thepredetermined filter coefficient and converting the second digitalsignal on the basis of the correcting filter coefficient and generatinga second converted signal on which the skew is corrected.

According to the ninth aspect of the present invention, a recordingmedium for recording a program used for a waveform generating moduleoutputting a pair of synchronous analog signals is provided, wherein thewaveform generating module comprises a DA converter for converting afirst and second digital signals into a first and second analog signalsat a predetermined time interval respectively, and the program allowsthe waveform generating module to function with a first digital signalcalculating unit for generating the first digital signal on the basis ofa first signal frequency component representing a component of eachfrequency of the first analog signal, which should be outputted by thewaveform generating module a second digital signal calculating unit forgenerating the second digital signal on the basis of a second signalfrequency component representing a component of each frequency of thesecond analog signal, which should be outputted by the waveformgenerating module a skew frequency component calculating unit forcalculating a skew frequency component representing a phase error ofeach frequency of the second analog signal corresponding to the firstanalog signal, on the basis of the skew of a timing with which the firstand second digital signals are converted by the DA converter and asecond signal frequency component correcting unit for correcting thesecond signal frequency component used for generating the second digitalsignal by the second digital signal calculating unit, on the basis ofthe skew frequency component.

According to the tenth aspect of the present invention, a waveformgenerating method for outputting a pair of synchronous analog signals,comprises the steps of generating a first digital signal on the basis ofa first signal frequency component representing a component of eachfrequency of a first analog signal, which should be outputted,generating a second digital signal on the basis of a second signalfrequency component representing a component of each frequency of asecond analog signal, which should be outputted, converting the firstand second digital signals into the first and second analog signals at apredetermined time interval respectively, calculating a skew frequencycomponent representing a phase error of each frequency of the secondanalog signal corresponding to the first analog signal, on the basis ofa skew of a timing with which the first and second digital signals areconverted during the step of converting and correcting the second signalfrequency component used for generating the second digital signal duringthe step of generating the second digital signal, on the basis of theskew frequency component.

According to the eleventh aspect of the present invention, a recordingmedium for recording a program used for a waveform generating moduleoutputting a pair of synchronous analog signals is provided, wherein thewaveform generating module comprises a DA converter for converting afirst and second digital signals into a first and second analog signalsat a predetermined time interval respectively, and the program allowsthe waveform generating module to function with a first digital filterfor generating a first converted signal into which a first digitalsignal, which represents a signal value of the first analog signal to beoutputted, is converted on the basis of a first filter coefficient, asecond digital filter for generating a second converted signal intowhich a second digital signal, which represents a signal value of thesecond analog signal to be outputted, is converted on the basis of asecond filter coefficient and a correcting filter coefficient generatorfor generating the second filter coefficient correcting a skew, besidesa waveform of an impulse response of the correcting filter coefficientis same as the first digital filter, on the basis of the skew of atiming with which the first and second digital signals converted intothe first and second analog signals by the DA converter and the firstfilter coefficient.

According to the twelfth aspect of the present invention, a waveformgenerating method for outputting a pair of synchronous analog signals,comprises the steps of generating a first converted signal into which afirst digital signal, which represents a signal value of a first analogsignal to be outputted, is converted on the basis of a first filtercoefficient, generating a second converted signal into which a seconddigital signal, which represents a signal value of a second analogsignal to be outputted, is converted on the basis of a second filtercoefficient, converting the first and second digital signals into thefirst and second analog signals at a predetermined time intervalrespectively and generating the second filter coefficient correcting askew, besides a waveform of an impulse response of the second filtercoefficient is same as the first digital filter, on the basis of theskew of a timing with which the first and second digital signalsconverted into the first and second analog signals during the step ofconverting and the first filter coefficient.

The summary of the invention does not necessarily describe all necessaryfeatures of the present invention. The present invention may also be asub-combination of the features described above. The above and otherfeatures and advantages of the present invention will become moreapparent from the following description of the embodiments taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a configuration of a digitizer apparatus 100 relating tothe first exemplary embodiment of the present invention.

FIG. 2 shows a process flow of a digitizer apparatus 100 relating to thefirst exemplary embodiment of the present invention.

FIG. 3 shows a configuration of a waveform generating apparatus 300relating to the second exemplary embodiment of the present invention.

FIG. 4 shows a process flow of a waveform generating apparatus 300relating to the second exemplary embodiment of the present invention.

FIG. 5 shows a configuration of a digitizer apparatus 500 relating tothe third exemplary embodiment of the present invention.

FIG. 6 shows a process flow of a digitizer apparatus 500 relating to thethird exemplary embodiment of the present invention.

FIG. 7 shows a configuration of a waveform generating apparatus 700relating to the fourth exemplary embodiment of the present invention.

FIG. 8 shows a process flow of a waveform generating apparatus 700relating to the fourth exemplary embodiment of the present invention.

FIG. 9 shows an exemplary hardware configuration of a digitizerapparatus 100, a waveform generating apparatus 300, a digitizerapparatus 500 and/or a waveform generating apparatus 700 relating to anexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on the preferred embodiments,which do not intend to limit the scope of the present invention, butexemplify the invention. All of the features and the combinationsthereof described in the embodiments are not necessarily essential tothe invention.

FIG. 1 shows a configuration of a digitizer apparatus 100 relating tothe first exemplary embodiment of the present invention. The digitizerapparatus 100 converts a pair of analog signals to be observed insynchronized state into a pair of digital signals with equal sampletiming. The digitizer apparatus 100, with regard to this conversion,corrects an error from sample timing with which a pair of analog signalsis converted into digital signals by a digital process so that animpairment of quality of signal can be prevented during digitizing apair of analog signals. The digitizer apparatus 100 includes an analoginput unit 101, an AD converter 110 and a correcting process unit 120.

The analog input unit 101 inputs an analog I input signal and an analogQ input signal in quadrature each other, an example of a pair of analogsignals to be observed in the synchronized state. The analog input unit101 includes a reference signal generator 102 a multiplexer 104, amultiplexer 105, a first analog unit 106 and a second analog unit 108.

The reference signal generator 102 generates a reference signal, whichthe correcting process unit 120 uses to measures a skew, an error oftiming with which a pair of analog signals are sampled by the ADconverter 110. The multiplexer 104 and the multiplexer 105 input thesame reference signal to the AD converter 110 via the first analog unit106 or the second analog unit 108, in case the digitizer apparatus 100measures the skew. And, in case that the digitizer apparatus 100 samplesthe analog I input signal and the analog Q input signal, The multiplexer104 and the multiplexer 105 input these signals to the AD converter 110via the first analog unit 106 or the second analog unit 108. The firstanalog unit 106 and the second analog unit 108 are an analog circuit,which input the analog I input signal and the analog Q input signal fromthe multiplexer 104 or the multiplexer 105, for example conduct aconversion of signal level and input the signals to the AD converter110.

The AD converter 110 samples a pair of analog signals inputted via theanalog input unit 101 with a sampling interval, a predetermined timeinterval, and converts the signals into a first digital signal and asecond digital signal. The AD converter 110 includes a reference clockgenerator 112, a first AD converter 114 and a second AD converter 116.

The reference clock generator 112 generates a sampling clock signalrepresenting sampling timing with which the first AD converter 114 andthe second AD converter 116 sample a pair of analog signals inputtedfrom the analog input unit 101. The first AD converter 114 converts theanalog I input signal into a digital I signal, an example of the firstdigital signal on the basis of the sampling clock signal. The second ADconverter 116 converts the analog Q input signal into a digital Qsignal, an example of the second digital signal on the basis of thesampling clock signal.

The correcting process unit 120 corrects an error of sample timing withrespect to a pair of digital signals and outputs a pair of digitalsignals with equal sample timing. The correcting process unit 120includes a first signal frequency component calculating unit 122, asecond signal frequency component calculating unit 124, a skew frequencycomponent calculating unit 126, a first signal frequency correcting unit128, a second signal frequency correcting unit 130, a skew measuringunit 132, a corrected first signal calculating unit 140 and a correctedsecond signal calculating unit 142.

The first signal frequency component calculating unit 122 calculates Isignal frequency components, an example of first signal frequencycomponents representing components of each frequency of the digital Isignal, on the basis of the digital I signal. The second signalfrequency component calculating unit 124 calculates Q signal frequencycomponents, an example of second signal frequency componentsrepresenting components of each frequency of the digital Q signal, onthe basis of the digital Q signal. More particularly, the first signalfrequency component calculating unit 122 and the second signal frequencycomponent calculating unit 124 may calculate the I signal frequencycomponents or the Q signal frequency components, the digital I signal orthe digital Q signal in frequency domain, by performing discreteFourier-transform of the digital I signal or the digital Q signal oftime domain respectively.

The skew frequency component calculating unit 126 calculates skewfrequency components representing phase errors of each frequency of thedigital Q signal with respect to the digital I signal, on the basis of askew of sampling timing with which a pair of analog signals is sampledby the AD converter 110. More particularly, the skew frequency componentcalculating unit 126 may calculate a correcting function in thefrequency domain correcting the skew with the frequency components.

The second signal frequency correcting unit 130 converts components ateach frequency with the same sample timing as the I signal frequencycomponents, by correcting the Q signal frequency components on the basisof the skew frequency components calculated by the skew frequencycomponent calculating unit 126. More particularly, the a second signalfrequency correcting unit 130 may correct the Q signal frequencycomponents by multiplying the Q signal frequency components by thecorrecting function in the frequency domain calculated by the skewfrequency component calculating unit 126. And, the second signalfrequency correcting unit 130 may correct the Q signal frequencycomponents on the basis of the skew frequency components and the Isignal frequency components.

The first signal frequency correcting unit 128 converts components ateach frequency with the same sample timing as the Q signal frequencycomponents, by correcting the I signal frequency components on the basisof the skew frequency components calculated by the skew frequencycomponent calculating unit 126. More particularly, the a first signalfrequency correcting unit 128 may correct the I signal frequencycomponents by multiplying the I signal frequency components by thecorrecting function in the frequency domain calculated by the skewfrequency component calculating unit 126. And, the first signalfrequency correcting unit 130 may correct the I signal frequencycomponents on the basis of the skew frequency components and the Qsignal frequency components. Here, in case that the second signalfrequency correcting unit 130 completely corrects the skew componentswith respect to the Q signal frequency components, the first signalfrequency correcting unit 128 may, without changing the I signalfrequency components, output to the corrected first signal calculatingunit 140.

The skew measuring unit 132 measures the skew of sampling timing withwhich a pair of analog signals inputted to the digitizer apparatus 100is sampled by the AD converter 110, and provides the skew to the skewfrequency component calculating unit 126. The skew measuring unit 132relating to the exemplary embodiment of the present invention measuresthe skew on the basis of an amount of a phase difference between thedigital I signal and the digital Q signal outputted from the first ADconverter 114 and the second AD converter 116, in case the samereference signal generated by the reference signal generator 102 withrespect to a pair of analog signals is inputted to the AD converter 110.

The corrected first signal calculating unit 140 calculates and outputscorrected digital I signal on which the skew is corrected on the basisof the I signal frequency components corrected by the first signalfrequency correcting unit 128. More particularly, the corrected firstsignal calculating unit 140 converts the I signal frequency components,spectrums of the digital I signal in the frequency domain, corrected bythe first signal frequency correcting unit 128, into the correcteddigital I signal in the time domain by, for example, performing theinverse discrete Fourier-transform. The corrected second signalcalculating unit 142, like the corrected first signal calculating unit140, calculates and outputs corrected digital Q signal on which the skewis corrected on the basis of the Q signal frequency components correctedby the second signal frequency correcting unit 130.

Next, an exemplary method for correcting the skew will be described withregard to the digitizer apparatus 100.

Letting i(t) and q(t) be the analog I signal and the analog Q signal inthe time domain respectively, which is inputted to the digitizerapparatus 100, pi(t) and pq(t) be each sampling clock signal of theanalog I signal and the analog Q signal, T be an sampling interval ofthe first AD converter 114 and the second AD converter 116 and τ be theskew of the first AD converter 114 and the second AD converter 116,pi(t) and pq(t) can be represented as the following equations (1) and(2) respectively: $\begin{matrix}{{p_{i}(t)} = {\sum\limits_{k = {- \infty}}^{\infty}{\delta\left( {t - {kT}} \right)}}} & (1) \\{{p_{q}(t)} = {\sum\limits_{k = {- \infty}}^{\infty}{{\delta\left( {t - {kT} - \tau} \right)}.}}} & (2)\end{matrix}$

If i(t) and q(t) is sampled using pi(t) and pq(t) with regard to thefirst AD converter 114 and the second AD converter 116, iskew(t) andqskew(t), a sampled digital I signal and a sampled digital Q signalincluding skew components, are the following equations (3) and (4)respectively: $\begin{matrix}{{i_{skew}(t)} = {{i(t)}{\sum\limits_{k = {- \infty}}^{\infty}{\delta\left( {t - {kT}} \right)}}}} & (3) \\{{q_{skew}(t)} = {{q(t)}{\sum\limits_{k = {- \infty}}^{\infty}{{\delta\left( {t - {kT} - \tau} \right)}.}}}} & (4)\end{matrix}$

If the Fourier-transform is performed of iskew(t) and qskew(t) withregard to the first signal frequency component calculating unit 122 andthe second signal frequency component calculating unit 124, the I signalfrequency components Iskew(f) and the Q signal frequency componentsQskew(f) are the following equations(5) and (6) respectively:$\begin{matrix}{{I_{skew}(f)} = {{{I(f)}*\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}{\delta\left( {f - \frac{k}{T}} \right)}}} = {\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}{I\left( {f - \frac{k}{T}} \right)}}}}} & (5) \\\begin{matrix}{{Q_{skew}(f)} = {{Q(f)}*e^{{- 2}\quad\pi\quad f\quad\tau}\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}{\delta\left( {f - \frac{k}{T}} \right)}}}} \\{= {\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}{{Q\left( {f - \frac{k}{T}} \right)}{{\mathbb{e}}^{{- j}\quad 2\quad\pi\quad k\quad{\tau/T}}.}}}}}\end{matrix} & (6)\end{matrix}$

Here, letting x(t)=i(t)+j·q(t), a complex signal in the time domaininputted to the digitizer apparatus 100, and X(f)=I(f)+j·Q(f), theFourier-transform of x(t), Xskew(f), a complex signal in the frequencydomain outputted by the first signal frequency component calculatingunit 122 and the second signal frequency component calculating unit 124,is the following equation(7): $\begin{matrix}\begin{matrix}{{X_{skew}(f)} = {{I_{skew}(f)} + {j\quad{Q_{skew}(f)}}}} \\{= {{\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}{I\left( {f - \frac{k}{T}} \right)}}} + {j\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}{{Q\left( {f - \frac{k}{T}} \right)}{{\mathbb{e}}^{{- j}\quad 2\quad\pi\quad k\quad{\tau/T}}.}}}}}}\end{matrix} & (7)\end{matrix}$

Here, using X(f) and X*(f), the conjugate function of X(f), I(f) andQ(f) are represented as the following equations(8) and (9) respectively:$\begin{matrix}{{I(f)} = {\frac{1}{2}\left\{ {{X(f)} + {X^{*}\left( {- f} \right)}} \right\}}} & (8) \\{{j\quad{Q(f)}} = {\frac{1}{2}{\left\{ {{X(f)} - {X^{*}\left( {- f} \right)}} \right\}.}}} & (9)\end{matrix}$

From equations(7) and (9), the following equation(10) is derived:$\begin{matrix}\begin{matrix}{{X_{skew}(f)} = {\frac{1}{2T}{\sum\limits_{k = {- \infty}}^{\infty}\left\lbrack {{X\left( {f - \frac{k}{T}} \right)} + {X^{*}\left( {{- f} + \frac{k}{T}} \right)} + {\left( {{X\left( {f - \frac{k}{T}} \right)} - {X^{*}\left( {{- f} + \frac{k}{T}} \right)}} \right){\mathbb{e}}^{{- j}\quad 2\quad\pi\quad k\quad{\tau/T}}}} \right\rbrack}}} \\{= {\frac{1}{2T}{\sum\limits_{k = {- \infty}}^{\infty}{\left\lbrack {{{X\left( {f - \frac{k}{T}} \right)}\left( {1 + {\mathbb{e}}^{{- j}\quad 2\quad\pi\quad k\quad{\tau/T}}} \right)} + {{X^{*}\left( {{- f} + \frac{k}{T}} \right)}\left( {1 - {\mathbb{e}}^{{- j}\quad 2\quad\pi\quad k\quad{\tau/T}}} \right)}} \right\rbrack.}}}}\end{matrix} & (10)\end{matrix}$

For example, considering the discrete Fourier-transform for k=0 or k=1with regard to the first signal frequency component calculating unit 122and the second signal frequency component calculating unit 124, Iskew(f)and Qskew(f), on the basis of equations.(5), (6), (8) and (9), are thefollowing equations(11) and (12) respectively: $\begin{matrix}{{I_{skew}(f)} = {\frac{1}{2T}\left\{ {{X(f)} + {X^{*}\left( {- f} \right)} + {X\left( {f - \frac{1}{T}} \right)} + {X^{*}\left( {{- f} + \frac{1}{T}} \right)}} \right\}}} & (11) \\\begin{matrix}{{j\quad{Q_{skew}(f)}} = {\frac{1}{2T}\left\{ {{X(f)} - {X^{*}\left( {- f} \right)} +} \right.}} \\{\left. {\left( {{X\left( {f - \frac{1}{T}} \right)} - {X^{*}\left( {{- f} + \frac{1}{T}} \right)}} \right){\mathbb{e}}^{{- j}\quad 2\quad\pi\quad{\tau/T}}} \right\}.}\end{matrix} & (12)\end{matrix}$

In order to eliminate a term X*(−f+1/T) for k=1 from equations(11) and(12), it is corrected that Qskew(f) is multiplied by ej2πτ/T. Here,Xc(f), a corrected complex signal in the frequency domain, usingequation(10) for k=0 or k=1, can be represented as the followingequation(13): $\begin{matrix}\begin{matrix}{{X_{c}(f)} = {{I_{skew}(f)} + {j\quad{\mathbb{e}}^{j\quad 2\quad\pi\quad{\tau/T}}{Q_{skew}(f)}}}} \\{\frac{1}{2}\left\lbrack {{X_{skew}(f)} + {X_{skew}^{*}\left( {- f} \right)} +} \right.} \\\left. {\left\{ {{X_{skew}(f)} - {X_{skew}^{*}\left( {- f} \right)}} \right\}{\mathbb{e}}^{j\quad 2\quad\pi\quad{\tau/T}}} \right\rbrack \\{= {\frac{1}{2}\left\lbrack {{{X_{skew}(f)}\left( {1 + {\mathbb{e}}^{j\quad 2\quad\pi\quad{\tau/T}}} \right)} + {{X_{skew}^{*}\left( {- f} \right)}\left( {1 - {\mathbb{e}}^{j\quad 2\quad\pi\quad{\tau/T}}} \right)}} \right\rbrack}} \\{= {{{\mathbb{e}}^{j\quad 2\quad\pi\quad{\tau/T}}\left\lbrack {{{X_{skew}(f)}{\cos\left( {\pi\quad{\tau/T}} \right)}} - {j\quad{X_{skew}^{*}(f)}{\sin\left( {\pi\quad{\tau/T}} \right)}}} \right\rbrack}.}}\end{matrix} & (13)\end{matrix}$

Here, performing the inverse Fourier-transform of [] part inequation(13), the following equation(10) is derived: $\begin{matrix}\begin{matrix}{\begin{matrix}{{Inv}\quad{Fourier}\left\{ \left\lbrack {{{X_{skew}(f)}\quad\cos\quad\left( {\pi\quad{\tau/T}} \right)} -} \right. \right.} \\\left. \left. {{{jX}_{skew}^{*}\left( {- f} \right)}\quad\sin\quad\left( {\pi\quad{\tau/T}} \right)} \right\rbrack \right\}\end{matrix} = {{{\cos\left( {\pi\quad{\tau/T}} \right)}{x_{skew}(t)}} -}} \\{j\quad{\sin\left( {\pi\quad{\tau/T}} \right)}{x_{skew}^{*}(t)}} \\{= {{\cos\left( {\pi\quad{\tau/T}} \right)}\left\{ {{i_{skew}(t)} +} \right.}} \\{\left. {{jq}_{skew}(t)} \right\} -} \\{j\quad{\sin\left( {\pi\quad{\tau/T}} \right)}\left\{ {{i_{skew}(t)} -} \right.} \\\left. {{jq}_{skew}(t)} \right\} \\{= \left\{ {{{i_{skew}(t)}{\cos\left( {\pi\quad{\tau/T}} \right)}} -} \right.} \\{\left. {{q_{skew}(t)}{\sin\left( {\pi\quad{\tau/T}} \right)}} \right\} +} \\{\left\{ {{{q_{skew}(t)}{\cos\left( {\pi\quad{\tau/T}} \right)}} -} \right.} \\\left. {{i_{skew}(t)}{\sin\left( {\pi\quad{\tau/T}} \right)}} \right\} \\{= {{i^{\prime}(t)} + {{{jq}^{\prime}(t)}.}}}\end{matrix} & (14)\end{matrix}$

I′ (t) and q′ (t) in equation(10) represent signals, which deviate froma rectangular coordinate of the digital I signal and the digital Qsignal and are in angular rotation on the basis of τ. That is to say,the digital I signal and the digital Q signal are analyzed withconverting to I′ axis and Q′ axis in a coordinate system in which thedigital I signal and the digital Q signal are in angular rotation on thebasis of τ. In order to adjust I′ axis in regard to equation(14) to Iaxis, Xc(f) is changed to the following equation(15):X _(c)(f)=e ^(−j2πτ/T) [I _(skew)(f)+je ^(2πτ/T) Q _(skew)(f)]  (15 ).

Equation(15) is applied to the discrete Fourier-transform. Here, thediscrete Fourier-transform of xskew(t) is the following equation(16):$\begin{matrix}\begin{matrix}{\left\lbrack {\int_{- \infty}^{\infty}{{X_{skew}(t)}{\mathbb{e}}^{{- 2}\quad\pi\quad{ft}}{\mathbb{d}t}}} \right\rbrack_{f = {k/{NT}}} = {\int_{- \infty}^{\infty}\left\{ {{{i_{skew}(t)}{p_{i}(t)}} +} \right.}} \\{\left. {{q_{skew}(t)}{p_{q}(t)}} \right\}{\mathbb{e}}^{{- j}\quad 2\quad\pi\quad{ft}}{\mathbb{d}t}} \\{= {{\sum\limits_{m = 0}^{N - 1}{{i_{skew}({mT})}{\mathbb{e}}^{{- j}\quad 2\quad\pi\quad{{kt}/N}}}} +}} \\{{\mathbb{e}}^{{- j}\quad 2\quad\pi\quad{{kt}/{NT}}}{\sum\limits_{m = 0}^{N - 1}{q_{skew}({mT})}}} \\{{\mathbb{e}}^{{- j}\quad 2\quad\pi\quad{{km}/N}}} \\{= {{{DFT}_{1}(k)} + {{\mathbb{e}}^{{- j}\quad 2\quad\pi\quad{{kt}/{NT}}}{{{DFT}_{0}(k)}.}}}}\end{matrix} & (16)\end{matrix}$

From equations(15) and (16), the following equation(17) is derived:$\begin{matrix}\begin{matrix}{{X\left( \frac{k}{NT} \right)} = {{\mathbb{e}}^{{- j}\quad\pi\quad{\tau/T}}\left\lbrack {{{DFT}_{I}(k)} + {{\mathbb{e}}^{j\quad 2\quad\pi\quad{\tau/T}}{\mathbb{e}}^{{- j}\quad 2\quad\pi\quad k\quad{\tau/{NT}}}{{DFT}_{Q}(k)}}} \right\rbrack}} \\{= {{{\mathbb{e}}^{{- j}\quad\pi\quad{\tau/T}}\left\lbrack {{{DFT}_{I}(k)} + {{\mathbb{e}}^{j\quad 2\quad\pi\quad{{\tau{({1 - {k/N}})}}/T}}{{DFT}_{Q}(k)}}} \right\rbrack}.}}\end{matrix} & (17)\end{matrix}$

That is, in case equation (17) is provided, the first signal frequencycomponent calculating unit 122 and the second signal frequency componentcalculating unit 124 perform the discrete Fourier-transform of thedigital I signal and the digital Q signal outputted by the first ADconverter 114 and the second AD converter 116 and calculate DFTI(k) andDFTQ(k), the I signal frequency components and the Q signal frequencycomponents, respectively. The skew frequency component calculating unit126 calculates a pair of skew frequency components of e−jπτ/T andej2πτ(1−k/N)/T on the basis of the skew τ. The first signal frequencycorrecting unit 128 and the second signal frequency correcting unit 130calculate corrected I signal frequency components and corrected Q signalfrequency components on the basis of the skew frequency components.Therefore, The first signal frequency correcting unit 128 and the secondsignal frequency correcting unit 130 can calculate equation(17).

And, in case the analog I input signal and the analog Q input signal aresuch as base band signals, a band, the digitizer apparatus 100 shouldmanage, is within ±nyquist frequency. Here, in case the band is limitedwithin the nyquist frequencies, equations corresponding to a negativeinput signal frequency, which multiply components for k=1, that is,spectrums between the nyquist frequency and a sampling frequency bycorrecting coefficiency ej2πτ/T 1 resulting from equation (13) ismultiplied by j·Qskew(f), are the following equations(18-1) and (18-2):0≦k<N/2(0˜nyquist frequency)$\begin{matrix}{{X\left( \frac{k}{NT} \right)} = {{{DFT}_{I}(k)} + {{\mathbb{e}}^{{- j}\quad 2\quad\pi\quad k\quad{\tau/{NT}}}{{DFT}_{Q}(k)}}}} & \left( {18\text{-}1} \right)\end{matrix}$  N/2≦k<N(nyquist frequency˜sampling frequency)$\begin{matrix}\begin{matrix}{{X\left( \frac{k}{NT} \right)} = {{{DFT}_{I}(k)} + {{\mathbb{e}}^{j\quad 2\quad\pi\quad{\tau/T}}{\mathbb{e}}^{{- j}\quad 2\quad\pi\quad k\quad{\tau/{NT}}}{{DFT}_{Q}(k)}}}} \\{= {{{DFT}_{I}(k)} + {{\mathbb{e}}^{j\quad 2\quad\pi\quad{{\tau{({1 - {k/N}})}}/T}}{{{DFT}_{Q}(k)}.}}}}\end{matrix} & \left( {18\text{-}2} \right)\end{matrix}$

Moreover, in this regards, the correcting process unit 120 may use the Isignal frequency components and the Q signal frequency componentsoutputted by the first signal frequency correcting unit 128 and thesecond signal frequency correcting unit 130 as a pair of digital signalswith equal sample timing without the corrected first signal calculatingunit 140 and the corrected second signal calculating unit 142. And,instead of measuring the skew on the basis of the amount of a phasedifference between the digital I signal and the digital Q signaloutputted by the first AD converter 114 and the second AD converter 116,the skew measuring unit 132 may, in case the reference signal generator102 inputs the same reference signal to the AD converter 110, adjust anamount of the correction for an optimum skew by measuring the skew ofthe digital I signal and the digital Q signal outputted by the correctedfirst signal calculating unit 140 and the corrected second signalcalculating unit 142 after the correction, changing the amount of thecorrection for the skew set by the skew frequency component calculatingunit 126.

FIG. 2 shows a process flow of a digitizer apparatus 100 relating to thefirst exemplary embodiment of the present invention. First, in order tomeasure the skew of sample timing of the first AD converter 114 and thesecond AD converter 116, the reference signal generator 102 inputs thereference signal to the first AD converter 114 via the multiplexer 104and the first analog unit 106, while inputting the same reference signalto the second AD converter 116 via the multiplexer 105 and the secondanalog unit 108(S200). The first AD converter 114 and the second ADconverter 116 convert the reference signal inputted into the digital Isignal and the digital Q signal respectively(S210). The skew measuringunit 132 measures the skew on the basis of the amount of the phasedifference between the digital I signal and the digital Q signal(S220)And, the skew frequency component calculating unit 126 calculates theskew frequency components representing the phase errors of eachfrequency of the digital Q signal corresponding to the digital I signalon the basis of the skew measured by the skew measuring unit 132(S230).

Next, the AD converter 110 inputs the analog I signals via themultiplexer 104 and the first analog unit 106, while inputting theanalog Q signal via the multiplexer 105 and the second analog unit 108(S240). And, the first AD converter 114 and the second AD converter 116in the AD converter 110 sample the pair of analog signals inputted, andconvert to the digital I signal and digital Q signal respectively(S250).

Next, the first signal frequency component calculating unit 122calculates the I signal frequency components on the basis of the digitalI signal, and the second signal frequency component calculating unit 124calculates the Q signal frequency components on the basis of the digitalQ signal(S260). And, the first signal frequency correcting unit 128 andthe second signal frequency correcting unit 130 correct the I signalfrequency components and the Q signal frequency components on the basisof the skew frequency components calculated by the skew frequencycomponent calculating unit 126(S270). And, the corrected first signalcalculating unit 140 and the corrected second signal calculating unit142 calculate the corrected digital I signal and the corrected digital Qsignal on which the skew is corrected, on the basis of the corrected Isignal Frequency components and the corrected Q signal frequencycomponents(S280).

According to the digitizer apparatus 100 described above, the skew ofthe sampling timing with which a pair of analog signals are sampled bythe AD converter 110 can be corrected for a frequency band of thedigital signal sampled by the AD converter 110. In addition, a magnitudeof the skew during operation is measured by the reference signalgenerator 102 and the skew measuring unit 132 and the amount of thecorrection can be adjusted using the magnitude of the skew measured sothat the digitizer apparatus 100 with high precision can be achieved.

FIG. 3 shows a configuration of a waveform generating apparatus 300relating to the second exemplary embodiment of the present invention.The waveform generating apparatus 300 inputs a pair of digital inputsignals to be converted into analog signals synchronized, and convertsto and outputs a pair of analog signals synchronized. With regard to theconversion, the waveform generating apparatus 300 prevents an impairmentof quality of signal during converting a pair of digital input signalsto analog signals by correcting an error of converting timing with whicha pair of digital input signals are converted into analog signalsrespectively, with a digital process. The waveform generating apparatus300 includes a correcting process unit 320 and a DA converter 380.

The correcting process unit 320 inputs digital I input signal anddigital Q input signal in quadrature each other, an example of a pair ofdigital input signals to be converted to analog signals synchronized.The correcting process unit 320 includes a reference signal generator322, a skew measuring unit 323, a first signal frequency componentcalculating unit 324, a second signal frequency component calculatingunit 325, skew frequency component calculating unit 326, a first signalfrequency component correcting unit 328, a second signal frequencycomponent correcting unit 330, a first digital signal calculating unit332, a second digital signal calculating unit 334, a multiplexer 338 anda multiplexer 340.

The reference signal generator 322 generates a reference signal, whichthe skew measuring unit 323 uses to measure a skew, an error of timingwith which a pair of digital input signals are converted by the DAconverter 380. The skew measuring unit 323 measures the skew of thetiming with which a pair of digital signals outputted by the correctingprocess unit 320 to DA converter 380 are converted by the DA converter380, and provides the skew to the first signal frequency componentcalculating unit 324. The skew measuring unit 323, according to thisexemplary embodiment, inputs the same reference signal generated by thereference signal generator 322 with a pair of digital signals to the DAconverter 380 via the multiplexer 338 and the multiplexer 340. And, inthis case, the skew measuring unit 323 measures the skew on the basis ofan amount of a phase difference between an analog I signal and an analogQ signal, an example of a first analog signal and a second analog signaloutputted by a first DA converter 384 and a second DA converter 386 inthe DA converter 380.

The first signal frequency component calculating unit 324, aconfiguration of which is the same as the first signal frequencycomponent calculating unit 122 regarding FIG. 1, calculates I signalfrequency components on the basis of the digital I input signal, anoriginal data of the analog I signal to be outputted by the waveformgenerating apparatus 300. Here, the I signal frequency components are anexample of first signal frequency components and represent components ofeach frequency of the analog I signal to be outputted by the waveformgenerating apparatus 300. The second signal frequency componentcalculating unit 325, a configuration of which is the same as the secondsignal frequency component calculating unit 124 regarding FIG. 1,calculates Q signal frequency components on the basis of the digital Qinput signal, an original data of the analog Q signal to be outputted.Here, the Q signal frequency components are an example of second signalfrequency components and represent components of each frequency of theanalog Q signal to be outputted.

The skew frequency component calculating unit 326, a configuration ofwhich is the same as the skew frequency component calculating unit 126regarding FIG. 1, calculates skew frequency components representingphase errors of each frequency of the analog Q signal corresponding tothe analog I signal, on the basis of the skew of timing with which acorrected digital I signal and a corrected digital Q signal outputted bythe correcting process unit 320 are corrected by the DA converter 380.Here, the corrected digital I signal and the corrected digital Q signalare an example of a first digital signal and a second digital signal.More particularly, the skew frequency component calculating unit 326 maycalculate a correcting function in the frequency domain correcting theskew with the skew frequency components.

The second signal frequency component correcting unit 330, aconfiguration of which is the same as the second signal frequencycorrecting unit 130 regarding FIG. 1, corrects Q signal frequencycomponents, which the second digital signal calculating unit 334 uses togenerate a corrected digital Q signal, on the basis of the skewfrequency components calculated by the skew frequency componentcalculating unit 326. More particularly, the second signal frequencycomponent correcting unit 330 may correct the Q signal frequencycomponents by multiplying the Q signal frequency components by thecorrecting function in the frequency domain calculated by the skewfrequency component calculating unit 326. And, the second signalfrequency component correcting unit 330 may correct the Q signalfrequency components on the basis of the skew frequency components andthe I signal frequency components.

The first signal frequency component correcting unit 328, aconfiguration of which is the same as the first signal frequencycorrecting unit 128 regarding FIG. 1, corrects I signal frequencycomponents, which the first digital signal calculating unit 332 uses togenerate a corrected digital I signal, on the basis of the skewfrequency components calculated by the skew frequency componentcalculating unit 326. More particularly, the first signal frequencycomponent correcting unit 328 may correct the I signal frequencycomponents by multiplying the I signal frequency components by thecorrecting function in the frequency domain calculated by the skewfrequency component calculating unit 326. And, the first signalfrequency component correcting unit 328 may correct the I signalfrequency components on the basis of the skew frequency components andthe Q signal frequency components. Here, in case the second signalfrequency component correcting unit 330 completely corrects the skewcomponents with respect to Q frequency components, the first signalfrequency component correcting unit 328 may, without changing the Isignal frequency components, output to the first digital signalscalculating unit 332.

The first digital signal calculating unit 332, a configuration of whichis the same as the corrected first signal calculating unit 140 regardingFIG. 1, generating a corrected digital I signal on the basis of the Isignal frequency components. More particularly, the first digital signalcalculating unit 332 converts the I signal frequency components,spectrums of the digital I input signal in the frequency domaincorrected by the first signal frequency component correcting unit 328,into the corrected digital I signal in the time domain by, for example,performing the inverse discrete Fourier-transform. The second digitalsignal calculating unit 334, a configuration of which is the same as thecorrected second signal calculating unit 142 regarding FIG. 1,generating a corrected digital Q signal on which the skew is correctedlike the first digital signal calculating unit 332. The multiplexer 338and the multiplexer 340, in case the skew measuring unit 323 measuresthe skew, inputs the same reference signal to the DA converter 380.Meanwhile, in case the waveform generating apparatus 300 outputs theanalog I signal and the analog Q signal corresponding to the digital Iinput signal and the digital Q input signal, the corrected digital Isignal and the digital Q signal corrected by the first digital signalcalculating unit 332 and the second the digital signal calculating unit334 are inputted to DA converter 380.

The DA converter 380 converts the corrected digital I signal and thedigital Q signal into the analog I signal and the analog Q signal with apredetermined converting time interval respectively. The DA converter380 includes a reference clock generator 382, a first DA converter 384and a second DA converter 386.

The reference clock generator 382 generates a converting clock signalrepresenting timing with which a pair of corrected digital signalsinputted by the correcting process unit 320 are converted by the firstDA converter 384 and the second DA converter 386. The first DA converter384 converts the corrected digital I signal into the analog I signal onthe basis of the converting clock signal. The second DA converter 386converts the corrected digital Q signal into the analog Q signal on thebasis of the converting clock signal.

In this regard, description of a method for correcting the skewregarding the first signal frequency component calculating unit 324, thesecond signal frequency component calculating unit 325, the skewfrequency component calculating unit 326, the first signal frequencycomponent correcting unit 328 and the second signal frequency componentcorrecting unit 330 will be omitted, since the method is same asdescribed with regard to FIG. 1 using equations(1) to (18-2).

In addition, the correcting process unit 320 may not include the firstsignal frequency component calculating unit 324 and the second signalfrequency component calculating unit 325. In this case, the correctingprocess unit 320 may generate the corrected digital I signal and thecorrected digital Q signal on the basis of the I signal frequencycomponent and the Q signal frequency component inputted by the firstsignal frequency component correcting unit 328 and the second signalfrequency component correcting unit 330, and output to the DA converter380.

FIG. 4 shows a process flow of a waveform generating apparatus 300relating to the second exemplary embodiment of the present invention.First, In order to measure the skew of converting timing of the first DAconverter 384 and the second DA converter 386, the reference signalgenerator 3?2 inputs the same reference signal to the first DA converter384 and the second DA converter 386 via the multiplexer 338 and themultiplexer 340(S400). The first DA converter 384 and the second DAconverter 386 convert the reference signal inputted into the analog Isignal and the analog Q signal respectively (S410). The skew measuringunit 323 measures the skew on the basis of an amount of a phasedifference between the analog I signal and the analog Q signal (S420).And the skew frequency component calculating unit 326 calculates theskew frequency components representing phase errors of each frequency ofthe analog Q signal corresponding to the analog I signal on the basis ofthe skew measured by the skew measuring unit 323(S430).

Next, the first signal frequency component calculating unit 324 and thesecond signal frequency component calculating unit 325 input the digitalI input signal and the digital Q input signal to be converted into theanalog signals synchronized respectively(S440) And, the first signalfrequency component calculating unit 324 and the second signal frequencycomponent calculating unit 325 calculate the I signal frequencycomponents and the Q signal frequency components respectively on thebasis of the digital I input signal and the digital Q inputsignal(S450). Next, the first signal frequency component correcting unit328 and the second signal frequency component correcting unit 330correct the I signal frequency components and the Q signal frequencycomponents on the basis of the skew frequency components calculated bythe skew frequency component calculating unit 326(S460). Next, the firstdigital signals calculating unit 332 and the second digital signalscalculating unit 334 calculate the corrected digital I signal and thecorrected digital Q signal on which the skew is corrected on the basisof the corrected I signal frequency components and the Q signalfrequency components respectively (S470). And, the first DA converter384 and the second DA converter 386 convert the corrected digital Isignal and the corrected digital Q signal on which the skew is correctedinto the analog I signal and the analog Q signal respectively (S480).

According to the digitizer apparatus 100 described above, the skew ofthe sampling timing with which a pair of digital signals are sampled bythe AD converter 380 can be corrected for digital signals in frequencydomain corresponding to analog signals. In addition, a magnitude of theskew during operation is measured by the reference signal generator 102and the skew measuring unit 132 and the amount of the correction can beadjusted using the magnitude of the skew measured so that the digitizerapparatus 100 with high precision can be achieved.

FIG. 5 shows a configuration of a digitizer apparatus 500 relating tothe third exemplary embodiment of the present invention. The digitizerapparatus 500 converts a pair of synchronous analog signals to beobserved into a pair of digital signals with equal sample timing. Withregard to the conversion, the digitizer apparatus 500 prevents animpairment of quality of signal during digitizing a pair of analogsignals by correcting an error of sample timing with which a pair ofanalog signals are converted into digital signals respectively with adigital filter. The digitizer apparatus 500 includes an analog inputunit 101, an AD converter 110 and a correcting process unit 520.Description about the analog input unit 101 and the AD converter 110with regard to FIG. 5 will be omitted, since a configuration thereof isthe same as the analog input unit 101 and the AD converter 110 shown inFIG. 1.

The correcting process unit 520 corrects an error of converting timingand converts to a pair of digital signals with equal converting timing,while performing a predetermined filtering process on the pair ofdigital signals outputted by the AD converter 110. The correctingprocess unit 520 includes a first digital filter 522, a correctingfilter coefficient generator 526, a second digital filter 524 and a skewmeasuring unit 532.

The first digital filter 522 converts a digital I signal inputted by theAD converter 110, an example of a first digital signal, on the basis ofa predetermined filter coefficient and generates a converted digital Isignal, an example of a first converted signal. Here, the first digitalfilter 522 may have a filter coefficient with which performing thefiltering process such as a band-rejection filtering and a band-passfiltering on the digital I signal.

The correcting filter coefficient generator 526 generates a correctingfilter coefficient correcting the skew of the first AD converter 114 andthe second AD converter 116, besides a waveform of an impulse responseof the correcting filter coefficient is same as the first digital filter522, on the basis of the skew of timing with which a pair of analogsignals inputted to the analog input unit 101 are sampled by the ADconverter 110 and the filter coefficient set in the first digital filter522.

The second digital filter 524 converts a digital Q signal inputted bythe AD converter 110, an example of a second digital signal, on thebasis of a correcting filter coefficient generated by the correctingfilter coefficient generator 526 and generates a converted digital Qsignal, an example of a second converted signal.

The skew measuring unit 532 measures the skew of timing with which apair of analog signals inputted to the analog input unit 101 are sampledby the AD converter 110 and provides the skew to the correcting filtercoefficient generator 526. The skew measuring unit 532 according to thisexemplary embodiment, in case the same reference signal generated by thereference signal generator 102 with a pair of analog signals is inputtedto the AD converter 110, measures the skew on the basis of an amount ofa phase difference between the digital I signal and the digital Q signaloutputted by the first AD converter 114 and the second AD converter 116.

Next, an exemplary method for correcting the skew regarding thedigitizer apparatus 500 is described.

Here, it is assumed that the first digital filter 522 and the seconddigital filter 524 are FIR filter, where function h(t) denotes thefilter coefficient. In this case, the impulse response of the firstdigital filter 522, letting T be a sampling interval of the AD converter110 is represented as the following equation(19): $\begin{matrix}{{{h(t)}\quad{\sum\limits_{k = 0}^{N - 1}{\delta\quad\left( {t - {kT}} \right)}}} = {\sum\limits_{k = 0}^{N - 1}{{h({kT})}\quad\delta\quad{\left( {t - {kT}} \right).}}}} & (19)\end{matrix}$

Here, the filter coefficient of the first digital filter 522 ish(k·T)(k=0, 1, . . . , N−1).

The correcting filter coefficient generator 526 generates the correctingfilter coefficient correcting the skew τ, besides a waveform of theimpulse response of the correcting filter coefficient is same as thefirst digital filter 522, on the basis of the filter coefficient of thea first digital filter 522 and the skew τ. The impulse response of thesecond digital filter 524 by the correcting filter coefficient isrepresented as the following equation (20): $\begin{matrix}{{{h(t)}\quad{\sum\limits_{k = 0}^{N - 1}{\delta\left( {t - {kT} - \tau} \right)}}} = {\sum\limits_{k = 0}^{N - 1}{{h\left( {{kT} - \tau} \right)}\quad\delta\quad{\left( {t - {kT} - \tau} \right).}}}} & (20)\end{matrix}$

According to the correcting filter coefficient h(k·T−τ) shown inequation(20), the second digital filter 524 can correct the digital Qsignal delayed by the skew τ relative to the digital I signal to outputwith the same sampling timing as the digital I signal.

In addition, with regard to analog input unit 101 and the AD converter110, an error in amplitude and/or direct current components of outputvalue of the digital I signal against the digital Q signal and thedigital Q input signal against the analog I input signal may arise. Thatis, with regard to equation(20), an impulse function δ′ (t−kT−τ), wherethe error in amplitude and direct current components arise, isrepresented as the following equation(21):δ′(t−kT−τ)=αδ(t−kT−τ)+β  (21).

From equations(20) and (21), a filter function of the second digitalfilter 524 correcting the error in amplitude and direct currentcomponents is represented as the following equation(22): $\begin{matrix}\begin{matrix}{{\sum\limits_{k = 0}^{N - 1}{{h\left( {{kT} - \tau} \right)}\quad\frac{1}{\alpha}\left\{ {{\delta^{\prime}\left( {t - {kT} - \tau} \right)} - \beta} \right\}}} =} \\{{\sum\limits_{k = 0}^{N - 1}{\frac{1}{\alpha}{h\left( {{kT} - \tau} \right)}\quad{\delta^{\prime}\left( {t - {kT} - \tau} \right)}}} + {\sum\limits_{k = 0}^{N - 1}{\left( {- \frac{\beta}{\alpha}} \right)\quad h\quad\left( {{kT} - \tau} \right)}}}\end{matrix} & (22)\end{matrix}$

In order to correct the phase errors, the error in amplitude and theerror in direct current components with equation (22), the digitizerapparatus 500 may be configured as following. The skew measuring unit532 operates as an error measuring unit measuring the error in amplitudeα and the error in direct current components β as well as the phaseerror τ. The correcting filter coefficient generator 526 generates1/·h(kT−τ) in equation(22) as the correcting filter coefficient, whilegenerating integer components, the second term in equation(22), as apart of the correcting filter coefficient. The second digital filter 524converts the digital Q signal using equation (22) on the basis of thecorrecting filter coefficient generated by the correcting filtercoefficient generator 526 and generates the converted digital Q signal.

Here, with regard to the skew measuring unit 532 operating as the errormeasuring unit, a difference between the output values of the digital Isignal and the digital Q signal, in case the reference signal that iszero in analog value inputted to the AD converter 110, may be the errorin direct current components β. And, a ratio of an average for amplitudeof the digital I signal and the digital Q signal, in case more than akind of the reference signal inputted to the AD converter 110, may bethe error in amplitude α.

FIG. 6 shows a process flow of a digitizer apparatus 500 relating to thethird exemplary embodiment of the present invention.

First, in order to measure the skew of the sample timing of the first ADconverter 114 and the second AD converter 116, the reference signalgenerator 102 inputs the reference signal to the first AD converter 114via the multiplexer 104 and the first analog unit 106 and inputs thesame reference signal to the second AD converter 116 via the multiplexer105 and the second analog unit 108(S600). The first AD converter 114 andthe second AD converter 116 convert the reference signal inputted intothe digital I signal and the digital Q signal respectively (S610). Theskew measuring unit 532 measures the skew on the basis of an amount ofthe phase difference between the digital I signal and the digital Qsignal (S620).

Next, the correcting filter coefficient generator 526 generates thecorrecting filter coefficient correcting the skew, besides the waveformof the impulse response of the correcting filter coefficient is same asthe first digital filter 522, on the basis of the skew measured by theskew measuring unit 132 and the filter coefficient set in the firstdigital filter 522(S630).

Next, the AD converter 110 inputs the analog I signal via themultiplexer 104 and the first analog unit 106, while inputting theanalog Q signal via the multiplexer 105 and the second analog unit108(S640). And, the first AD converter 114 and the second AD converter116 in the AD converter 110 sample a pair of analog signals inputted andconvert to the digital I signal and the digital Q signal respectively(S650).

Next, the first digital filter 522 converts the digital I signalinputted by the first AD converter 114 on the basis of the predeterminedthe filter coefficient and generates the converted digital I signal.And, the first digital filter 522 converts the digital Q signal inputtedby the AD converter 110 on the basis of the correcting filtercoefficient generated by the correcting filter coefficient generator 526and generates the converted digital Q signal (S660).

According to the digitizer apparatus 500 described above, the skew ofsampling with which a pair of analog signals are sampled by the ADconverter 110 can be corrected by changing at least one of a pair of thefilter coefficients used for filtering a pair of digital signalssampled. And, a magnitude of the skew during operation is measured bythe reference signal generator 102 and the skew measuring unit 532 andthe correcting filter coefficient can be adjusted using the magnitude ofthe skew measured so that the digitizer apparatus 500 with highprecision can be achieved.

FIG. 7 shows a configuration of a waveform generating apparatus 700relating to the fourth exemplary embodiment of the present invention.The waveform generating apparatus 700 inputs a pair of digital inputsignals to be converted into analog signals, which should besynchronized, and converts and outputs a pair of analog signalssynchronized. With regard to this conversion, the waveform generatingapparatus 700 prevents the impairment of quality of signal duringconverting a pair of digital input signal into analog signals bycorrecting an error of converting timing with which a pair of digitalinput signal are converted into the analog signals respectively by adigital filter. The waveform generating apparatus 700 includes acorrecting process unit 720 and a DA converter 380. Description aboutthe DA converter 380 regarding FIG. 7 is omitted, since the DA converter380 has the same configuration as the DA converter 380 shown in FIG. 3.

The correcting process unit 720 inputs a digital I input signal and adigital Q input signal in quadrature each other, an example of a pair ofdigital input signals to be converted into the analog signalssynchronized. The correcting process unit 720 includes a referencesignal generator 722, a skew measuring unit 723, a first digital filter726, a correcting filter coefficient generator 724, a second digitalfilter 728, a multiplexer 730 and a multiplexer 732.

The reference signal generator 722, which has the same configuration asthe reference signal generator 322, generates a reference signal, whichthe skew measuring unit 723 uses to measure a skew of timing with whicha pair of digital input signals are converted by the DA converter 380.The skew measuring unit 723, which has the same configuration as thereference signal generator 323, measures the skew of timing with which apair of digital signal outputted by the correcting process unit 720 tothe DA converter 380 are converted by the DA converter 380, and providesthe skew to the correcting filter coefficient generator 724. The skewmeasuring unit 723 according to this exemplary embodiment, in case thesame reference signal generated by the reference signal generator 722 isinputted to the DA converter 380, measure the skew on the basis of anamount of a phase difference between a analog I signal and a analog Qsignal outputted by the first DA converter 384 and the second DAconverter 386 in the DA converter 380, an example of the first analogsignal and the second analog signal.

The first digital filter 726, which has the same configuration as thefirst digital filter 522 regarding FIG. 5, converts the digital I inputsignal representing a signal value of the analog I signal to beoutputted by the waveform generating apparatus 700 on the basis of apredetermined first filter coefficient, and generates a converteddigital I signal, an example of a first converted signal.

The correcting filter coefficient generator 724, which has the sameconfiguration as the correcting filter coefficient generator 526regarding FIG. 5, generates a second filter coefficient correcting theskew, besides a waveform of the impulse response of the second filtercoefficient is same as the first digital filter 522, on the basis of theskew of timing with which the analog I signal and the analog Q signalare converted by the DA converter 380 and a first filter coefficient,and sets in the second digital filter 728.

The second digital filter 728, which has the same configuration as thesecond digital filter 524 regarding FIG. 5, converts the digital Q inputsignal representing a signal value of the analog Q signal to beoutputted by the waveform generating apparatus 700 on the basis of asecond filter coefficient, and generates a converted digital Q signal,an example of a second converted signal.

The multiplexer 730 and the multiplexer 732 input the same referencesignal to the DA converter 380, in case the skew measuring unit 723measures the skew. Meanwhile, in case the waveform generating apparatus700 outputs an analog I signal and an analog Q signal corresponding tothe digital I input signal and the digital Q input signal via the DAconverter 380, the converted digital I signal and the converted digitalQ signal are inputted to the DA converter 380.

FIG. 8 shows a process flow of a waveform generating apparatus 700relating to the fourth exemplary embodiment of the present invention.

First, in order to measure the skew of converting timing of the first DAconverter 384 and the second DA converter 386, the reference signalgenerator 722 inputs the same reference signal to the first DA converter384 and the second DA converter 386 via the multiplexer 730 and themultiplexer 732(S800). The first DA converter 384 and the second DAconverter 386 convert the reference signal inputted into the analog Isignal and the analog Q signal respectively (S810). The skew measuringunit 723 measures the skew on the basis of an amount of the phasedifference between the analog I signal and the analog Q signal (S820).And, the correcting filter coefficient generator 724 generates thesecond filter coefficient correcting the skew, besides the waveform ofthe impulse response of the second filter coefficient is same as thefirst digital filter 522, on the basis of the skew measured by the skewmeasuring unit 723 and the first filter coefficient, and sets in thesecond digital filter 728(S830).

Next, the first digital filter 726 and the second digital filter 728input the digital I input signal and the digital Q input signalrespectively, which should be converted into the analog signalssynchronized (S840). The first digital filter 726 converts the digital Iinput signal on the basis of the first filter coefficient, and generatesthe converted digital I signal. The second digital filter 728 convertsthe digital Q input signal on the basis of the second filter coefficientgenerated by the correcting filter coefficient generator 724, andgenerates the converted digital Q signal (S850). The first DA converter384 and the second DA converter 386 convert the converted digital Isignal and the converted digital Q signal on which the skew is correctedinto the analog I signal and the analog Q signal respectively (S860).

In this regard, description of a method for correcting the skewregarding the correcting filter coefficient generator 724, the firstdigital filter 726 and the second digital filter 728 will be omitted,since the method is same as described with regard to FIG. 6 usingequations (19) and (20).

According to the digitizer apparatus 700 described above, the skew ofsampling with which the DA converter 380 converts to a pair ofsynchronous analog signals can be corrected by digital filtering digitalsignals corresponding to the analog signals to be outputted in thefrequency domain. And, a magnitude of the skew during operation ismeasured by the reference signal generator 722 and the skew measuringunit 723 and an amount of the correction can be adjusted using themagnitude of the skew measured so that the digitizer apparatus 700 withhigh precision can be achieved.

FIG. 9 shows an exemplary hardware configuration of a digitizerapparatus 100, a waveform generating apparatus 300, a digitizerapparatus 500 and/or a waveform generating apparatus 700 relating to anexemplary embodiment of the present invention. The digitizer apparatus100, the waveform generating apparatus 300, the digitizer apparatus 500and/or the waveform generating apparatus 700, according to thisexemplary embodiment of the present invention, include a CPU 900, a ROM910, a RAM 920, a communication interface 930, a hard disc driver 940, aflexible disc driver 950 and a CD-ROM driver 960, and are implemented bythe information processing apparatus 890 coupled to the AD converter 110and/or the DA converter 380 via the analog input unit 101

The CPU 900 operates on the basis of programs installed in the ROM 910and the RAM 920, and controls each parts. The ROM 910 contains a bootprogram executed by the CPU 900 when the information processingapparatus 890 drives or programs depending on hardware of theinformation processing apparatus 890. The RAM 920 contains programsexecuted by the CPU 900 and data used by the CPU 900. The communicationinterface 930 communicates other apparatuses via communication networks.The hard disc driver 940 contains programs and data used by theinformation processing apparatus 890 and provides the programs and datato the CPU 900 via RAM 920. The flexible disc driver 950 reads programsor data from a flexible disc 990 and provides the programs or data tothe RAM 920. The CD-ROM driver 960 reads programs or data from a CD-ROM995 and provides the programs or data to the RAM 920.

Programs provided to the CPU 900 via the RAM 920 are contained in arecording medium such as the flexible disc 990, the CD-ROM 995 or a ICcard and provided to a user. The programs are read from the recordingmedium, installed in the information processing apparatus 890 via theRAM 920 and executed for the information processing apparatus 890.

A program, which is installed in the information processing apparatus890, executed and allows the information processing apparatus 890 tofunction as the digitizer apparatus 100, includes a first signalfrequency component calculating module, a second signal frequencycomponent calculating module, a skew frequency component calculatingmodule, a first signal frequency correcting module, a second signalfrequency correcting module, a skew measuring module, a corrected firstsignal calculating module and a corrected second signal calculatingmodule. These program or modules allow the information processingapparatus 890 to function as a first signal frequency componentcalculating unit 122, a second signal frequency component calculatingunit 124, a skew frequency component calculating unit 126, a firstsignal frequency correcting unit 128, a second signal frequencycorrecting unit 130, a skew measuring unit 132, a corrected first signalcalculating unit 140 and a corrected second signal calculating unit 142respectively.

A program, which is installed in the information processing apparatus890, executed and allows the information processing apparatus 890 tofunction as the waveform generating apparatus 300, includes a referencesignal generating module, a skew measuring module, a first signalfrequency component calculating module, a second signal frequencycomponent calculating module, a skew frequency component calculatingmodule, a first signal frequency component correcting module, a secondsignal frequency component correcting module, a first digital signalcalculate module and a second digital signal calculate module. Theseprogram or modules allow the information processing apparatus 890 tofunction as a reference signal generator 322, a skew measuring unit 323,a first signal frequency component calculating unit 324, a second signalfrequency component calculating unit 325, a skew frequency componentcalculating unit 326, a first signal frequency component correcting unit328, a second signal frequency component correcting unit 330, a firstdigital signal calculating unit 332 and a second digital signalcalculating unit 334 respectively.

A program, which is installed in the information processing apparatus890, executed and allows the information processing apparatus 890 tofunction as the digitizer apparatus 500, includes a first digital filtermodule, a second digital filter module, a correcting filter coefficientgenerating module and a skew measuring module. These program or modulesallows the information processing apparatus 890 to function as a firstdigital filter 522, a second digital filter 524, a correcting filtercoefficient generator 526 and a skew measuring unit 532 respectively.

A program, which is installed in the information processing apparatus890, executed and allows the information processing apparatus 890 tofunction as the waveform generating apparatus 700, includes a referencesignal generating module, a skew measuring module, a correcting filtercoefficient generating module, a first digital filter module and seconddigital filter module. These program or modules allows the informationprocessing apparatus 890 to function as a reference signal generator722, a skew measuring unit 723, a correcting filter coefficientgenerator 724, a first digital filter 726 and a second digital filter728.

The programs and modules described above may be contained an externalrecording medium. As the recording medium, an optical recording mediumsuch as a DVD or a PD as well as the flexible disc 990 and the CD-ROM995, an optical magnetic recording medium such as MD, a tape medium andsemiconductor memory such as the IC card can be used. And, the programsmay be provided from an external network to the information processingapparatus 890 via the communication network by using memory devices suchas a hard disc or a RAM installed in a server system connected to aleased communication network or internet as the recording medium.

Although the present invention has been described by way of exemplaryembodiments, it should be understood that those skilled in the art mightmake many changes and substitutions without departing from the spiritand the scope of the present invention, which is defined by the appendedclaims.

For example, a pair of analog input signals inputted by the digitizerapparatus 100 or the digitizer apparatus 500 or a pair of analog signalsgenerated by the waveform generating apparatus 300 or the waveformgenerating apparatus 700 are not limited to quadrature signals and maybe any kinds of synchronous analog signals.

It is apparent from the description above that, according to the presentinvention, a difference of sample timing or converting timing between apair of signals to be synchronized is suppressed so that a digitizermodule, a waveform generating module, a converting method and a waveformgenerating method, preventing an impairment of quality of signal, and arecording medium for recording a program thereof can be achieved.

1-6. (Canceled)
 7. A digitizer module for converting a pair of analogsignals into a pair of digital signals with equal sample timing,comprising: an AD converter for sampling said pair of analog signals ata predetermined time interval and converting into a first and a seconddigital signals; a first digital filter for generating a first convertedsignal into which said first digital signal is converted on the basis ofa predetermined filter coefficient; a correcting filter coefficientgenerator for generating a correcting filter coefficient correcting askew, besides a waveform of an impulse response of said correctingfilter coefficient is same as said first digital filter, on the basis ofsaid skew of a timing with which said pair of analog signals are sampledby said AD converter and a predetermined filter coefficient; and asecond digital filter for converting said second digital signal on thebasis of said correcting filter coefficient and generating a secondconverted signal on which said skew is corrected.
 8. A digitizer moduleas claimed in claim 7, wherein said correcting filter coefficientgenerator makes said correcting filter coefficient be h(k·T−τ), in casesaid predetermined filter coefficient is h(k·T) and said skew is τ,where said first digital filter has at least two said predeterminedfilter coefficient, k denotes an integer in a range of zero to a numberone less than the number of said predetermined filter coefficient and Tdenotes a sampling interval of said AD converter. 9-17. (Canceled)
 18. Arecording medium for recording a program used for a digitizer moduleconverting a pair of analog signals into a pair of digital signals withequal sample timing, wherein said digitizer module comprises an ADconverter for sampling said pair of analog signals at a predeterminedtime interval and converting said pair of analog signals into a firstand second digital signals, and said program allows said digitizermodule to function with: a first digital filter for generating a firstconverted signal into which said first digital signal is converted onthe basis of a predetermined filter coefficient; a correcting filtercoefficient generator for generating a correcting filter coefficientcorrecting a skew, besides a waveform of an impulse response of saidcorrecting filter coefficient is same as said first digital filter, onthe basis of said skew of a timing with which said first and secondanalog signals are converted by said AD converter and said predeterminedfilter coefficient; and a second digital filter for converting saidsecond digital signal on the basis of said correcting filter coefficientand generating a second converted signal on which said skew iscorrected.
 19. A converting method for converting a pair of analogsignals into a pair of digital signals with equal sample timing,comprising the steps of: sampling said pair of analog signals at apredetermined time interval and converting said pair of analog signalsinto a first and second digital signals respectively; generating a firstconverted signal into which said first digital signal is converted onthe basis of a predetermined filter coefficient; generating a correctingfilter coefficient correcting a skew, besides a waveform of an impulseresponse of said correcting filter coefficient is same as said step ofgenerating said first converted signal, on the basis of said skew of atiming with which said first and second analog signals are converted bysaid AD converter and said predetermined filter coefficient; andconverting said second digital signal on the basis of said correctingfilter coefficient and generating a second converted signal on whichsaid skew is corrected.
 20. -
 23. (Canceled)